Lady Shay had an issue with this guy and she used her pee to communicate how she felt. She did not like the fact that the guy was doing things that she did not approve of and he did not change or correct himself when she warned him against doing those things. He had no choice but to change when he noticed that she would not tolerate his nonsense anymore.
Lady Shay did not like how freaky this guy was and she was not comfortable continuing to have fun with him. She wanted him to realize that he was grossing her out and so the mistress peed on him. He was shocked at why she was doing it but at first he thought that she was trying a new fetish with her but that was not the case as he came to find out.